There is known a vehicle seat having a structure in which a seat back includes a top plate main part for supporting a body of a seated person from the rear side and a top plate side part for supporting the body of the seated person from both outer sides (JP-U-H05-076860). The seat back has a configuration in which the left and right top plate side parts form a continuous shell-like shape independent from the top plate main part and can be moved rearward with respect to the top plate main part when getting on and off the vehicle.
In the above technology, the support for the body of the seated person from the rear side is performed only by the top plate main part. Therefore, it is difficult to appropriately receive an excessive load received from the body of the seated person at the time of occurrence of a collision or the like of the vehicle. The disclosure has been made as a solution to the above problem and an object to be achieved by the disclosure is to make it possible to appropriately receive an excessive load applied to the seat back from the body of the seated person at the time of occurrence of a collision or the like of a vehicle.